An indexable ball-end mill of the two-blade type has been generally known in the related art. However, the market demand for a ball-end mill capable of cutting a workpiece with higher efficiency is developing. In response to the demand, an indexable ball-end mill of the three-blade type is currently proposed. In the ball-end mill of this type, three cutting edges are involved in cutting. Therefore, the ball-end mill of the three-blade type can perform machining with higher efficiency than that of the ball-end mill of the two-blade type.
Patent Literature 1 exemplifies an indexable ball-end mill that can be used as a ball-end mill of a three-blade type. Referring to paragraph [0027] and FIG. 9 of Patent Literature 1, it is suggested that a ball-end mill may be of a three-blade type including two inserts functioning as outer peripheral cutting edges and one insert functioning as a central cutting edge. The two inserts functioning as the outer peripheral cutting edges are of the same kind, and further, each of them has cutting edges at top and bottom surfaces thereof. Therefore, it is suggested that if one of the two cutting edges is abraded, each of the inserts may be turned over at its original mount position of the ball-end mill or the other outer peripheral cutting edges may be switched over.